SpaceX Thread

How far up does the first stage usually take? And what percentage of fuel? I would think that catching a 2nd stage in orbit would almost be like catching a bullet.

You seem to be envisioning something quite completely different from what's being described.

The second stage typically goes into orbit and then either brakes to reenter or goes into some parking orbit where it just contributes to the orbital debris problem. A tanker or tug can refuel it or haul it off so it can return to Earth or go elsewhere in the solar system...perhaps being converted into another tanker or tug. No catching bullets involved, and the first stage's fuel load is rather irrelevant.

Heatshielding on the shuttle and other re-entry vehicles was ablatative, something like high tensile ceramics.

This makes me wonder if Aerogel (http://en.wikipedia.org/wiki/Aerogel) could withstand the extreme temps of re-entry to be viable. Or would it be insufficiently strong to take the atmospheric buffetting?

How far up does the first stage usually take? And what percentage of fuel? I would think that catching a 2nd stage in orbit would almost be like catching a bullet.

You seem to be envisioning something quite completely different from what's being described.

The second stage typically goes into orbit and then either brakes to reenter or goes into some parking orbit where it just contributes to the orbital debris problem. A tanker or tug can refuel it or haul it off so it can return to Earth or go elsewhere in the solar system...perhaps being converted into another tanker or tug. No catching bullets involved, and the first stage's fuel load is rather irrelevant.

I still believe it would be like catching a bullet, when you consider the size of the field (the entire night sky!) in which a rocket must launch and then catch up to a 2nd stage in orbit to boost up and get to a higher point, unless after the first stage is burnt up you are willing to wait for a day or more to catch up to a 2nd stage. You would have to time the launch window to coincide with the 2nd stage...very difficult IMO.

I still believe it would be like catching a bullet, when you consider the size of the field (the entire night sky!) in which a rocket must launch and then catch up to a 2nd stage in orbit to boost up and get to a higher point, unless after the first stage is burnt up you are willing to wait for a day or more to catch up to a 2nd stage. You would have to time the launch window to coincide with the 2nd stage...very difficult IMO.

Has it occurred to you that this is exactly what happens every time something docks with the ISS?

How far up does the first stage usually take? And what percentage of fuel? I would think that catching a 2nd stage in orbit would almost be like catching a bullet.

You seem to be envisioning something quite completely different from what's being described.

The second stage typically goes into orbit and then either brakes to reenter or goes into some parking orbit where it just contributes to the orbital debris problem. A tanker or tug can refuel it or haul it off so it can return to Earth or go elsewhere in the solar system...perhaps being converted into another tanker or tug. No catching bullets involved, and the first stage's fuel load is rather irrelevant.

Typically, for LEO spacecraft, the 2nd stage gets very close to the final orbit of its payload. The satellite (in this case Dragon) uses its own thrusters to get some separation from upper stage, then the upper stage fires small retro rockets to put it in a collapsing orbit to keep there from being too much debris. It doesn't take a lot of delta-V to get back down from a low parking orbit.

The shuttle did something similar to lose the external tank. With the shuttle, at SSME shutdown the shuttle wasn't in a stable orbit, the OMS were used to circularize the orbit and raise perigee out of the atmosphere. The tank continued on its nominal trajectory, and re-entered the atmosphere. This can also be done with upper stages.

For other satellites, like GEO birds, the upper stage typically puts the satellite into an elliptical transfer orbit. Somewhere along the way, the satellite will separate from the upper stage. The upper stage can then fire retros to push its perigee back into the atmosphere while the satellite uses its thrusters to circularize its orbit.

As to putting upper stages into stable orbits for re-use later, capturing them is no different then docking with anything else... of course an empty stage is a non-cooperative target unless the decide to put a beacon and/or some control system on-board. Finding, tracking, and intercepting can be done, but its much easier when your target plays nice.

Heatshielding on the shuttle and other re-entry vehicles was ablatative, something like high tensile ceramics.

This makes me wonder if Aerogel (http://en.wikipedia.org/wiki/Aerogel) could withstand the extreme temps of re-entry to be viable. Or would it be insufficiently strong to take the atmospheric buffetting?

The Shuttle was one of very few vehicles not to use ablatives...it used tiles of a silica fiber material similar to aerogel in properties for the bulk of its shielding, with carbon-carbon composites on the leading edge. And neither ablatives nor the Shuttle TPS tiles could be described as "high tensile ceramics".

I still believe it would be like catching a bullet, when you consider the size of the field (the entire night sky!) in which a rocket must launch and then catch up to a 2nd stage in orbit to boost up and get to a higher point, unless after the first stage is burnt up you are willing to wait for a day or more to catch up to a 2nd stage. You would have to time the launch window to coincide with the 2nd stage...very difficult IMO.

Orbital rendezvous was first performed in 1965 and is now routine, and is nothing like catching a bullet. And given that you can deliver roughly double the payload to LEO with a given rocket that you can deliver to a geosynchronous transfer orbit, a LEO rendezvous with a second stage converted into a tug/refueling vehicle means doubling your payload to GTO...with plenty of available capacity left over, given the relatively small delta-v required to go from LEO to GSO. Yes, it requires a narrow launch window, but that rendezvous means you can send LEO-sized payloads across the solar system.

I still believe it would be like catching a bullet, when you consider the size of the field (the entire night sky!) in which a rocket must launch and then catch up to a 2nd stage in orbit to boost up and get to a higher point, unless after the first stage is burnt up you are willing to wait for a day or more to catch up to a 2nd stage. You would have to time the launch window to coincide with the 2nd stage...very difficult IMO.

Orbital rendezvous was first performed in 1965 and is now routine, and is nothing like catching a bullet. And given that you can deliver roughly double the payload to LEO with a given rocket that you can deliver to a geosynchronous transfer orbit, a LEO rendezvous with a second stage converted into a tug/refueling vehicle means doubling your payload to GTO...with plenty of available capacity left over, given the relatively small delta-v required to go from LEO to GSO. Yes, it requires a narrow launch window, but that rendezvous means you can send LEO-sized payloads across the solar system.

With the caveat that while it takes a relatively low delta-V to get from LEO to GEO, there are still time concerns due to the radiation belts. One example, the USAF AEHF satellite, uses conventional propulsion (i.e. chemical rockets) to inject into a high MEO transfer, then a kick motor to circularize above the upper edge of the outer Van Allen belt. From there it uses ion thrusters which are high efficiency / low thrust to spiral out to GEO. This was done to minimize the time spent exposed to high energy particles in the radiation belt.

A space-tug would likely need to perform the same sort of maneuver - fast transfer through the radiation belts followed by a more relaxed, continuous thrust maneuver to the final orbit.

With the caveat that while it takes a relatively low delta-V to get from LEO to GEO, there are still time concerns due to the radiation belts. One example, the USAF AEHF satellite, uses conventional propulsion (i.e. chemical rockets) to inject into a high MEO transfer, then a kick motor to circularize above the upper edge of the outer Van Allen belt. From there it uses ion thrusters which are high efficiency / low thrust to spiral out to GEO. This was done to minimize the time spent exposed to high energy particles in the radiation belt.

A space-tug would likely need to perform the same sort of maneuver - fast transfer through the radiation belts followed by a more relaxed, continuous thrust maneuver to the final orbit.

In my opinion chemical is better for mid to lower earth orbits. To avoid a slow spiral through the Van Allen Belts, as you say. Also near earth perigees are very brief, an ion thruster with minute thrust can't enjoy the full Oberth benefit. And if you're delivering a commodity, trip times of a few days are better than trip times lasting several months. That is one reason I'm excited about a source of oxygen and hydrogen at EML1. That would be the perfect propellant for cislunar space.

A ship would hang about the neighborhood of a heliocentric orbit's perihelion much longer, giving an ion engine the time it needs for a substantial burn. Ion is much better for deep space destinations, in my opinion.

I still believe it would be like catching a bullet, when you consider the size of the field (the entire night sky!) in which a rocket must launch and then catch up to a 2nd stage in orbit to boost up and get to a higher point, unless after the first stage is burnt up you are willing to wait for a day or more to catch up to a 2nd stage. You would have to time the launch window to coincide with the 2nd stage...very difficult IMO.

Orbital rendezvous was first performed in 1965 and is now routine, and is nothing like catching a bullet. And given that you can deliver roughly double the payload to LEO with a given rocket that you can deliver to a geosynchronous transfer orbit, a LEO rendezvous with a second stage converted into a tug/refueling vehicle means doubling your payload to GTO...with plenty of available capacity left over, given the relatively small delta-v required to go from LEO to GSO. Yes, it requires a narrow launch window, but that rendezvous means you can send LEO-sized payloads across the solar system.

When I say "catching a bullet" I mean it would be roughly analogous to the anti-missile system that, last I read, was about hitting a ballistic missile with a missile. I mean, yes Space X reached the space station but it did take them a day to reach it. And if the 2nd stage is not met in time it's likely that the craft might see its orbit decay.

I'm trying to find a diagram that shows the size/weight/propellant of a typical first stage relative to the altitude it reaches in the earth's atmo. Anyone?

When I say "catching a bullet" I mean it would be roughly analogous to the anti-missile system that, last I read, was about hitting a ballistic missile with a missile.

Not really the same thing at all.

A rendezvous means you know the current orbit and location of object A. An orbit implies you also know the mass, elevation, and velocity of object A. Given that you know the mass of object B, you then simply need to calculate the elevation/velocity and launch/burn time in order to match up. You can get "close enough" to adapt from there. You have very low closing delta-v, and have plenty of time to make course corrections. You *also* don't have that pesky atmosphere causing unwanted changes to your speed and direction.

Missile interception is an entirely different problem...firstly you can't assume you know anything about it's course. Second, you have to create an insanely high delta-v for it to be of any use. Third, you must have enough fuel to keep making course corrections. Finally, a missile is very, very small target...typically moving very fast *towards* you. An orbiting object simply keeps floating around in a big, lazy circle or ellipse...in a very predictable fashion.

With the caveat that while it takes a relatively low delta-V to get from LEO to GEO, there are still time concerns due to the radiation belts. One example, the USAF AEHF satellite, uses conventional propulsion (i.e. chemical rockets) to inject into a high MEO transfer, then a kick motor to circularize above the upper edge of the outer Van Allen belt. From there it uses ion thrusters which are high efficiency / low thrust to spiral out to GEO. This was done to minimize the time spent exposed to high energy particles in the radiation belt.

A space-tug would likely need to perform the same sort of maneuver - fast transfer through the radiation belts followed by a more relaxed, continuous thrust maneuver to the final orbit.

The radiation belts are only relevant for long-term lifetime of spacecraft and for manned missions. There's numerous satellites that orbit in or through the hottest parts of the belts...basically everything lower than geosynchronous orbit and higher than LEO.

The Air Force wasn't trying to avoid the belts with AEHF 1, they were trying to get out of the transfer orbit with malfunctioning propulsion systems. The Liquid Apogee Engine was supposed to put it in something very close to GEO, with the Hall thrusters used for final adjustments. The LAE failed, so they used chemical reaction thrusters (apparently intended for steering the craft during the LAE burn) to get perigee clear of Earth's atmospheric drag and reduce the time required, and finished the job with Hall thrusters. Those thrusters actually only raised perigee to 4700 km, still inside the hottest part of the inner belt, and reduced inclination from 22.1 degrees to 15.1 degrees, further aligning the plane of the orbit with the belts. It then did multiple firings of the Hall thrusters to slowly raise perigee right through both belts over the course of 9 months.

When I say "catching a bullet" I mean it would be roughly analogous to the anti-missile system that, last I read, was about hitting a ballistic missile with a missile.

It's not even remotely analogous to an anti-missile system. It's analogous to Gemini 6 and 7 in 1965, 8 and the Agena in 1966, Cosmos 186-188, Soyuz 4-5, Apollo-Soyuz, all of the many space station transfers of crew and cargo and station assembly missions, Apollo moon landings, Shuttle satellite recovery and repair missions, and so on. Once again, orbital rendezvous is routine.

sophistry wrote:

And if the 2nd stage is not met in time it's likely that the craft might see its orbit decay.

SpaceX in fact took several days to do tests of the Dragon craft before rendezvous with the ISS. And if it takes a day, so what? How often is it worth hundreds of millions for a larger rocket to get to orbit a day earlier?

sophistry wrote:

And if the 2nd stage is not met in time it's likely that the craft might see its orbit decay.

That's why they plan orbital launches out ahead of time rather than just throwing multimillion to multibillion dollar payloads onto the rocket and figuring out what to do as they go along.

sophistry wrote:

I'm trying to find a diagram that shows the size/weight/propellant of a typical first stage relative to the altitude it reaches in the earth's atmo. Anyone?

Anyone know if their multistage recoverability plan is possible? The whole "first stage falls back down, executes controlled burn to land on skids, second stage deorbits with a quick burn and heat shield deceleration, executes another controlled burn to land on skids" thing?

IIRC NASA had several vehicle concepts that were supposed to do things like this.

When I say "catching a bullet" I mean it would be roughly analogous to the anti-missile system that, last I read, was about hitting a ballistic missile with a missile.

It's not even remotely analogous to an anti-missile system. It's analogous to Gemini 6 and 7 in 1965, 8 and the Agena in 1966, Cosmos 186-188, Soyuz 4-5, Apollo-Soyuz, all of the many space station transfers of crew and cargo and station assembly missions, Apollo moon landings, Shuttle satellite recovery and repair missions, and so on. Once again, orbital rendezvous is routine.

sophistry wrote:

And if the 2nd stage is not met in time it's likely that the craft might see its orbit decay.

SpaceX in fact took several days to do tests of the Dragon craft before rendezvous with the ISS. And if it takes a day, so what? How often is it worth hundreds of millions for a larger rocket to get to orbit a day earlier?

sophistry wrote:

And if the 2nd stage is not met in time it's likely that the craft might see its orbit decay.

That's why they plan orbital launches out ahead of time rather than just throwing multimillion to multibillion dollar payloads onto the rocket and figuring out what to do as they go along.

sophistry wrote:

I'm trying to find a diagram that shows the size/weight/propellant of a typical first stage relative to the altitude it reaches in the earth's atmo. Anyone?

It depends on the rocket. How is this at all relevant?

Orbital rendevous at the end of a 1st stage? The shuttle went through 2 stages before reaching its operational height. Here we're talking about having one stage go up and then rendezvous with a 2nd stage already in orbit, refuel it, and then progress to the final destination...

While leaving a 2nd stage in space would IMO lead to 20-50% more height/payload, meet an existing stage in the short window that it's available, getting it to point in the right direction (it would likely be in whichever direction after orbiting the earth), and making it to the final destination...not to mention the risks of some unknown breakdown occurring on the 2nd stage while it is in orbit...

So SpaceX's heavy dragon rocket looks interesting in that it has a linked fuel system so that when the booster rockets are spent, the main rocket will have a full fuel load instead of having burnt some of its fuel in the initial ascent with the boosters. Impressive advancement. Along those lines, I don't think that they'll succeed in a soft landing of the first two stages, but instead will likely figure out a way to better "weatherize" the stages for reuse after like a week-long refurbishment.

Clearly not; the second stage must expend its propellant to achieve orbital velocity.

But if a satellite can be carried to orbit by the second stage, it's clearly also possible to carry a fuel container to orbit on top of the second stage. A fuel container is just another kind of satellite.

Then with the two craft in very similar orbits, a rendezvous is possible. It's not like trying to catch a bullet because the relative velocity is almost zero. It's more like trying to catch a bullet that hasn't been fired, and is sitting motionless on the ground in front of you.

Did you see the video of Dragon rendezvousing with the space station? The relative velocity was so slow as to be boring, it took hours to go a few hundred feet. I think what's going on here is that you either don't understand the science, or you do understand the science but your English isn't good enough to understand what people are talking about or express yourself clearly.

It doesn't appear to be in gross violation of physical law, but it is extremely challenging.

I'm fairly confident they can make it work, at least for the first stage; whether it really buys them a fast turnaround time or saves significant amounts of money remains to be seen.

I can see it working really well for the Heavy; since the outer cores will stage lower and slower than the central core, they should be easier to recover in this manner (still seems bloody damned difficult, but IANARS).

It doesn't appear to be in gross violation of physical law, but it is extremely challenging.

I'm fairly confident they can make it work, at least for the first stage; whether it really buys them a fast turnaround time or saves significant amounts of money remains to be seen.

I can see it working really well for the Heavy; since the outer cores will stage lower and slower than the central core, they should be easier to recover in this manner (still seems bloody damned difficult, but IANARS).

In the Grasshopper videos it shows stages 1 and 2 turning and doing a deceleration burn. It also shows use of reaction mass to do vertical landing. I would like to know much this adds to the delta V budget.

For a hover just above earth's surface, each 102 seconds costs 1 km/s in delta V.

It doesn't appear to be in gross violation of physical law, but it is extremely challenging.

I'm fairly confident they can make it work, at least for the first stage; whether it really buys them a fast turnaround time or saves significant amounts of money remains to be seen.

I can see it working really well for the Heavy; since the outer cores will stage lower and slower than the central core, they should be easier to recover in this manner (still seems bloody damned difficult, but IANARS).

In the Grasshopper videos it shows stages 1 and 2 turning and doing a deceleration burn. It also shows use of reaction mass to do vertical landing. I would like to know much this adds to the delta V budget.

For a hover just above earth's surface, each 102 seconds costs 1 km/s in delta V.

Orbital rendevous at the end of a 1st stage? The shuttle went through 2 stages before reaching its operational height. Here we're talking about having one stage go up and then rendezvous with a 2nd stage already in orbit, refuel it, and then progress to the final destination...

No. You are the only one talking about SSTO vehicles, and I have no idea where you're getting it from. How can you look at a post talking about refueling the second stage and think it's talking about SSTO?

The same basic principle does mean LEO refueling (or more likely, cargo transfer to an orbital tug) would turn SSTO from something that's barely maybe doable into something that might be useful. However, there's still a massive benefit from staging.

sophistry wrote:

While leaving a 2nd stage in space would IMO lead to 20-50% more height/payload, meet an existing stage in the short window that it's available, getting it to point in the right direction (it would likely be in whichever direction after orbiting the earth), and making it to the final destination...not to mention the risks of some unknown breakdown occurring on the 2nd stage while it is in orbit...

No, double the payload if the same sized rocket is used, potentially much more. A refueled second stage in LEO could easily take its full payload to GEO or beyond, and payload to LEO is roughly double payload to GEO. The transfer to GEO is a small fraction of the total delta-v required to reach orbit, and a second stage converted into a tug could transfer much larger payloads than it initially launched...meaning a Falcon 9 second stage converted into a tug could not only double the payload to GEO of another Falcon 9, it could double the payload of a much larger rocket. And once again, rendezvous and other orbital maneuvers are routinely done...you're seeing problems that don't exist. As for unknown breakdowns...the tug is proven, tested hardware that can do much of its part of the work (refueling itself, positioning in orbit) before the launch even occurs (no risk of it failing to start up because of an assembly error), and you can even have backup tugs in place in case of failure. Plus with the reduction in cost of mass to the desired orbit, you can have larger margins on the spacecraft itself. This doesn't increase risk at all, it makes a quite sizable reduction in them.

sophistry wrote:

So SpaceX's heavy dragon rocket looks interesting in that it has a linked fuel system so that when the booster rockets are spent, the main rocket will have a full fuel load instead of having burnt some of its fuel in the initial ascent with the boosters. Impressive advancement. Along those lines, I don't think that they'll succeed in a soft landing of the first two stages, but instead will likely figure out a way to better "weatherize" the stages for reuse after like a week-long refurbishment.

Actually, the Heavy variant looks quite promising for partial reuse. There'd still be a substantial benefit in payload over the single-core version when the boosters drop off early enough to return.

Megalodon wrote:

It doesn't appear to be in gross violation of physical law, but it is extremely challenging.

SpaceX does mention that there'll be a large reduction in payload due to the need for the first stage to shut down and separate early enough to return on land, and mass for reinforcement/shielding of the second stage...they're not being unrealistic about it. It's doable, but there are tradeoffs, and it's hard to say if they'll succeed at making money at it...they need low operational costs and a large number of relatively small-payload customers.

In the Grasshopper videos it shows stages 1 and 2 turning and doing a deceleration burn. It also shows use of reaction mass to do vertical landing. I would like to know much this adds to the delta V budget.

I think Musk said somewhere that it means they stage around mach 6 instead of mach 9. So that's on the order of 1 km/s delta-v available for return/landing (though obviously it won't be 1 km/s anymore because the next stage and payload will be gone).

In the Grasshopper videos it shows stages 1 and 2 turning and doing a deceleration burn. It also shows use of reaction mass to do vertical landing. I would like to know much this adds to the delta V budget.

I think Musk said somewhere that it means they stage around mach 6 instead of mach 9. So that's on the order of 1 km/s delta-v available for return/landing (though obviously it won't be 1 km/s anymore because the next stage and payload will be gone).

That's an extra km/second that you're now putting on the second stage plus the dragon. It may make first stage recovery easier but now you have a more difficult mass fraction for the remaining vehicle.

That's an extra km/second that you're now putting on the second stage plus the dragon. It may make first stage recovery easier but now you have a more difficult mass fraction for the remaining vehicle.

Seems to me, after watching the video, they were simply line-guides for the large chutes, to maintain the proper descent angle (and possibly provide additional surface area for the cabling to apply pressure to.) They were originally covered by heat shielding, which appears to have ablated, and thus allow the drogue chuts to pull everything nice and snug into a three-prong attachment cradle on the capsule. (attachment points one and two at the lower end of each of those 'cuts', and the third at the apex)

I believe what you are seeing there are channels underneath the ablative heatshield which contained lines for the parachutes. I imagine that a linear charge of some kind was used to cut the heatshield material after the vehicle was slowed to near terminal velocity, and the chutes were deployed. It sort of looks like the chutes were packed/stored near the bottom (fat) end of the craft, and were deployed from there, with lines running under the heatshield to the top where you'd like to anchor them.